Sleep apnea syndromes are seriously disabling sleep disorders. While these syndromes are induced by sleep, the sleep state -- REM or NREM-- is also a factor in the presence or absence of apnea. Marked pulmonary and femoral artery pressure changes occur during sleep in association with serious arrhythmias. Administration of atropine decreases the sinus bradycardia but has little effect on hemodynamic changes. A Shy-Drager patient with upper airway sleep apnea, however, did not demonstrate any change in femoral arterial pressure during sleep. This suggests direct involvement of the autonomic nervous system in the cardiac changes observed during upper airway sleep apnea. Tracheostomy eliminates excessive daytime sleepiness and greatly decreases the arrythmia and hemodynamic changes noted in upper airway sleep apnea patients. Myotonia dystrophic patients present a central sleep apnea syndrome with secondary excessive daytime sleepiness. During REM sleep, there is a worsening of apnea with cardiac arrhythmia.